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Failure to Infect Laboratory Rodent Hosts with Human Isolates of Rodentolepis (= Hymenolepis) Nana

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Failure to Infect Laboratory Rodent Hosts with Human Isolates of Rodentolepis (= Hymenolepis) Nana Journal of Helminthology (2002) 76, 37±43 DOI: 10.1079/JOH200198 Failure to infect laboratory rodent hosts with human isolates of Rodentolepis (= Hymenolepis) nana M.G. Macnish1, U.M. Morgan1, J.M. Behnke2 and R.C.A. Thompson1* 1WHO Collaborating Centre for the Molecular Epidemiology of Parasitic Infections and Division of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia: 2School of Life and Environmental Sciences, University of Nottingham, University Park, Nottingham, NG7 2RD, UK Abstract Confusion exists over the species status and host-specificity of the tapeworm Rodentolepis (= Hymenolepis) nana. It has been described as one species, R. nana, found in both humans and rodents. Others have identified a subspecies; R. nana var. fraterna, describing it as morphologically identical to the human form but only found in rodents. The species present in Australian communities has never been identified with certainty. Fifty one human isolates of Rodentolepis (= Hymenolepis) nana were orally inoculated into Swiss Q, BALB/c, A/J, CBA/ CAH and nude (hypothymic) BALB/c mice, Fischer 344 and Wistar rats and specific pathogen free (SPF) hamsters. Twenty four human isolates of R. nana were cross-tested in flour beetles, Tribolium confusum. No adult worms were obtained from mice, rats or hamsters, even when immunosuppressed with cortisone acetate. Only one of the 24 samples developed to the cysticercoid stage in T. confusum; however, when inoculated into laboratory mice the cysticercoids failed to develop into adult worms. The large sample size used in this study, and the range of techniques employed for extraction and preparation of eggs provide a comprehensive test of the hypothesis that the human strain of R. nana is essentially non-infective to rodents. Introduction There is confusion in the literature regarding both the nomenclature and host specificity of R. nana. A taxo- Rodentolepis (= Hymenolepis) nana is the most common nomic revision of hymenolepidids with armed rostellae cestode infecting humans worldwide (Smyth, 1994). (hooks present) was proposed by Spasskii in 1954 Estimates of the number of human infections range (Vaucher, 1992) in which Hymenolepis nana was reclassi- from 20 million (Andreassen, 1998) to 50±75 million fied under the genus Rodentolepis and this classification is (Pawlowski, 1984; Crompton, 1999) worldwide. Humans currently recognized by some cestode taxonomists may also be infected with the rat tapeworm, Hymenolepis (Czaplinski & Vaucher, 1994). The genus Hymenolepis diminuta, but this is considered rare and usually Weinland 1858 now only contains hymenolepidid species accidental (Schantz, 1996; Andreassen, 1998) and almost with unarmed rostellae (hooks absent) and the type always occurs in children (Tena et al., 1998). species is the rat tapeworm Hymenolepis diminuta (Czaplinski & Vaucher, 1994). Despite the revised *Author for correspondence nomenclature being adopted by some taxonomists Fax: (61 8) 9310 4144 (Spasskii, 1994; Czaplinski & Vaucher, 1994) Rodentolepis E-mail: [email protected] nana is almost universally referred to as Hymenolepis nana 38 M.G. Macnish et al. Table 1. Inoculation of SPF mice and flour beetles with human isolates of Rodentolepis (=Hymenolepis) nana. Samples yielding Number of Number of cysticercoids (beetles) Samples yielding SPF mice or beetles Species mice or beetles Sex Age samples tested or adult worms (mice) adult worms Swiss Q Mouse 85 Male 4±5 wks 51 0 0 BALB/c Mouse 98 Male 4±5 wks 51 0 0 BALB/c nude² Mouse 5 Male 4±5 wks 1 0 0 Flour beetles T. confusum 110 ND ND 11a 1* 0 Flour beetles T. confusum 130 ND ND 13b 00 a Eggs obtained by NaCl flotation. b Direct faecal feeding. * One sample yielded 73 cysticercoids dissected from five Tribolium confusum beetles infected via ad libitum feeding of eggs on filter paper. ² Hypothymic model. ND, not determined. in the medical literature. (cf. Arme & Pappas, 1983; Materials and methods Pawlowski, 1984; Smyth & McManus, 1989; Smyth, 1994; Baily, 1996; Schantz, 1996; Lloyd, 1998; Andreassen, Source of parasites 1998). A laboratory isolate of R. nana was kindly provided by In Australia, human infections with Rodentolepis (= Dr Akira Ito, Gifu University, Japan in two forms: (i) eggs Hymenolepis) nana are most common in communities in in PBS; and (ii) approximately 30 flour beetles, Tribolium tropical regions. The prevalence of R. nana has risen from confusum, infected with the cysticercoid stage of R. nana. 20% (Meloni et al., 1993) to approximately 55% in these The isolate has been passaged through laboratory mice same communities (Reynoldson et al., 1997) within the for more than 20 years. Human faecal samples were last decade. There is uncertainty about the transmission collected from the north-west region of Western Australia of R. nana in these endemic areas where human infection over a period of three years. Positive identification of is common. It is not well understood whether the `strain/ infection was carried out using the ZnSO4 flotation species' of R. nana present in the north-west of Western technique (Voge, 1970). Eggs were usually extracted from Australia is found in rodent and human hosts or whether faecal samples using the NaCl flotation method (Voge, humans harbour their own form of this parasite. For 1970) prior to inoculation into specific pathogen free example, R. nana has been described as being infective to (SPF) mice, rats and hamsters (tables 1 and 2). Other egg both humans and rodents (Yamaguti, 1959). Others have extraction techniques used in this study are outlined (see concluded that the rodent form is a subspecies, R. nana Infection methods tested using human isolates). var. fraterna, morphologically indistinguishable from the human form and only infective to rodents (cf. Baer & Tenora, 1970; Pawlowski, 1984; Schantz, 1996; Lloyd, Infection of mice and beetles using a laboratory reference strain 1998). In the present study, some of these uncertainties The direct and indirect life cycles of R. nana were tested were resolved by testing the infectivity of a number of in this study using eggs and cysticercoids sent by Dr Ito human isolates of R. nana in specific pathogen free (SPF) (Gifu University, Japan). Infected Tribolium confusum sent mice, rats and hamsters under varying conditions. by Dr Ito were killed and dissected using a WILD M7A Table 2. Cortisone acetate treatment regime in mice, rats and hamsters prior to inoculation with human isolates of Rodentolepis (=Hymenolepis) nana. SPF strain Species Number Sex Age Cortisone treatment Adult worms obtained Swiss Qa Mouse 3a/3* Male 4±5 wks 125 mg kg21; 5 dosesa 0 AJa Mouse 3a/3* Male 4±5 wks 125 mg kg21; 5 dosesa 0 CBA/CAHa Mouse 3a/3* Male 4±5 wks 125 mg kg21; 5 dosesa 0 AJb Mouse 3b/3* Male 4±5 wks 125 mg kg21; 5 dosesb 0 CBA/CAHb Mouse 3b/3* Male 4±5 wks 125 mg kg21; 5 dosesb 0 Fischer 344c Rat 3c/3* Male 4±5 wks 100 mg total in 2 dosesc 0 Wistarc Rat 3c/3* Male 4±5 wks 100 mg total in 2 dosesc 0 DSNd Hamsters 15d Male 8 wks 25 mg kg21 in 2 dosesd 0 a Cortisone injections days 2, 4, 6, 8, 10, 12 (dose-weight dependent). b Cortisone injections days -1, 1, 3, 5, 7, 9 (dose-weight dependent). c Cortisone injections days 4 and 6 (dose-weight independent). d Cortisone given to all 15 hamsters days -1 and 4. * Control group received no cortisone. Infectivity of human R. nana to rodents 39 stereo microscope (WILD Heerbrugg, Switzerland). use of a congenitally hypothymic mouse model (Ito, Cysticercoids were collected into phosphate buffered 1985). saline (PBS) and orally inoculated, via stomach tube, into 6. Feeding NaCl-extracted eggs to Tribolium confusum Swiss Quackenbush (Swiss Q) and BALB/c male, 4- to 5- (flour beetles) that were pre-starved for 6 days (Naka- week-old mice. Approximately 11 days later, adult mura & Okamoto, 1993) on either filter paper (Yan & worms were dissected from the small intestine and Norman, 1995) or a latex rubber sheet (Nakamura & washed repeatedly in PBS. Eggs were teased from the Okamoto, 1993). gravid proglottids from worms obtained in this manner 7. Feeding T. confusum (pre-starved for 6 days) directly on and routinely passaged through mice and beetles. In infected faeces (Pappas et al., 1995; Yan & Norman, 1995). addition, R. nana eggs sent by Dr Ito were stored in PBS at 48C and were periodically inoculated into mice (19, 23, 26, 62 and 70 days post-collection). This was primarily to Cortisone acetate treatment provide a positive control of the decline of viability of eggs stored at non-ambient temperatures over a several Five different strains of SPF mice were used for the week period. When mice were inoculated with eggs, experimental procedures including Swiss Q (Thompson, rather than cysticercoids, euthanasia and dissection were 1972; Seidel & Voge, 1975) BALB/c (Asano et al., 1986; delayed until day 14 due to the longer pre-patency of Watanabe et al., 1994; Matsuo & Okamoto, 1995); A/J and infection. CBA/CAH (Ito et al., 1988); two strains of SPF rats: Fischer 344 (Ito, 1983) and Wistar, an equivalent strain to the Rowett rats used by (Ito & Kamiyama, 1987) and SPF Infection of mice, rats and hamsters using human samples hamsters (Ronald & Wagner, 1975). The SPF mice and rats used in this study (tables 1 and 2) were purchased from the Animal Resources Centre Mice (ARC), Western Australia. The infection trials were Six Swiss Q, A/J and CBA/CAH mice were divided conducted at Murdoch University, Western Australia. into two equal groups. All mice were weighed prior to The hamster infection trial (table 2) was conducted by the trial to adjust their dose of cortisone accordingly. A J.M. Behnke with a human isolate of R.
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